The Chinese 24, 36, and 48 diode flat panel LEDs generally are accompanied by an adapter harness for T-10, festoon, and BA9s sockets but very seldom by an adaptor for BA15s. The few which are so accompanied are usually priced considerably higher (with shipping from Kowloon) than the 3+$ for the more usual offering.
I recently changed out Illuminaire aircraft style fixtures with BA15s sockets to Bargman dual fixtures with T-10 sockets. Worked out great with the available flat LED panels and the commonly available connector. Likewise with my range hood light
which was also T-10. I have three additional diffuser lights
in the trailer, one over sink, one on fwd cabinet side, and one in the loo. All are BA15s. I wasn't happy with the 360 degree stalk-type LEDs in these fixtures but hesitated because finding either adaptor harnesses or new BA15 bases is either very rare or very expensive per unit. There was a post here some time ago about an eBay buy of several of these but I decided that the price + shipping was really over the top.
I decided to attempt to salvage the bases from 1156 and 1141 bayonet type bulbs and the wire harness from the left over festoon and BA9 adaptors which accompany the Chinese bulbs. You will most likely have to solder your own harness to the base so an extra step to recycle a brass base is not that much more trouble.
Here's what I think is a safe and efficient method for removing the glass bulb and filament to retrieve the base. I first thought to use a "nutcracker" approach. Without going into great detail, let's say that I gave up on breaking the glass globe inside a plastic bag not so much because of the possibility of injury from broken or flying glass but because the remainder of the glued-in base was left behind. Late yesterday evening it occured to me that boiling the bulb in hot water might cause the cement around the glass to release. This proved to be the case and the glass globes released very easily and the leads from the bottom contact and shell were then the broken or twisted off. Please remember to place a lid over the boiling water in the very unlikely event that the glass globe ruptures violently. Wear eye protection. It only requires a few minutes in boiling water to make the cement release from the glass such that globe and base can be pulled apart.
I noticed in the expensive offering on the internet that the contact at the bottom had a hole. I made a hole in the contacts on my recycled bases by melting the solder, both creating the hole and pushing out the remaining conductor with a plastic push pin. From there it was very easy to push the stripped red conductor into the hole in the base contact, tin my iron, and melt the existing solder to make the join. Altho my extra BA9s harnesses came with the black conductor soldered to the inside of the shell, I found it very difficult to put enuf heat into the larger BA15 bases to get solder to cohere, so I remelted the large external blob that assures shell contact with the fixture and attached there. Even with these itty-bits, I did the soldering with no holding fixtures or alligator clips and only removed my glasses and squinted once, so it's really not that difficult. All three of the adaptor harnesses worked first time so I replaced "bulbs" in two of my old fixtures and reserved the additional harness for the time when I exhaust my supply of "stalk" type LEDs and need to use a flat panel in the shower.
I hope this will "light a bulb" for someone here and save them some head-scratching and dollars. Do be cautious how you approach the removal of the glass bulb from the base.